Self-storing lift gates of the general type with which the present invention is concerned, are known in the art, see for example McCarty U.S. Pat. No. 3,138,270, for example. Other patents showing lift gate assemblies of the general type with which the present invention is concerned are Robinson U.S. Pat. Nos. 3,429,464, Novotney 3,172,549, and Lugash 3,269,567, and others. In general, lift gates of this type include a pair of like parallelogram linkages having a relatively short fixed link on the frame and a second relatively short link which is mounted on the load lifting platform with two relatively long links, normally referred to as a compression link and a tension link, coupling the fixed frame link to the platform link. In the usual case, the tension link is provided with some sort of lost motion mechanism so that the platform link may be shifted to one or the other side of an over center position relative to the long links. When the platform is in one relationship to the linkage, the platform remains horizontal throughout the range of power driven movement of the parallelogram linkage to transfer loads between ground level and the level of the vehicle bed. When the platform is shifted manually into the opposite over center relationship, raising of the parallelogram linkage causes the platform to be folded into a compact generally parallel relationship with the long links of the linkage into a stored position underneath the truck bed.
In the usual case, to accommodate the shifting of the platform link to opposite sides of its respective over center relationship, the platform is so dimensioned as to pass freely between the pair of linkage assemblies and thus, when in its stored position, the platform is frequently supported only at the pivotal connections to the two long links of each pair with the platform cantilevered out from this point of support. The bouncing of the truck as it travels over uneven road surfaces causes the freely cantilevered platform to exert substantial impact forces on its pivotal mounting, with attendant rattling.
The present invention is especially designed to provide a lift gate of the general type described above in which the linkage is so arranged as to lie in underlying supporting reationship to the platform when the platform is in its stored position to fully support the platform assembly and to minimize rattling and the accompanying jarring road shock impacts on the lift linkage. Further, the present invention provides a novel latching mechanism which is operable to automatically latch the assembly in its stored position. While this problem has been recognized to some extent -- note the safety chain provided by McCarty 3,138,270, for example, the operator frequently forgets to attach the safety chains or may attach the chain only at one side of the assembly. The hydraulic system alone will not hold the assembly in the stored position because as a practical matter seepage or leakage within the hydraulic system is nearly always present.